1. Field of the Invention
This invention relates to a magnetic disk apparatus, for example, a magnetic-disk drive apparatus.
2. Description of the Related Art
Magnetic recording media include flexible magnetic disks. A typical flexible magnetic disk is used under conditions as follows. While the disk is rotated at a speed of 300 rpm, data are written thereon at a rate of 0.5 Mbps. Similarly, while the disk is rotated at a speed of 300 rpm, data are read therefrom at a rate of 0.5 Mbps.
There is a flexible magnetic disk of a special type. The data rate is equal to 0.417 Mbps in the case where data are read from the special disk while the disk is rotated at a speed of 300 rpm.
A prior-art drive for the typical disk is incapable of reading data from the special disk.
It is an object of this invention to provide an apparatus which can handle flexible magnetic disks different from each other in data rate.
A first aspect of this invention provides a magnetic disk apparatus comprising a spindle motor for rotating a magnetic disk;
first means for selectively generating either a first pulse-train signal or a second pulse-train signal which differs from the first pulse-train signal in pulse frequency; and second means for, when the first means generates the first pulse-train signal, controlling the spindle motor to rotate at a first rotational speed in response to the first pulse-train signal, and for, when the first means generates the second pulse-train signal, controlling the spindle motor to rotate at a second rotational speed in response to the second pulse-train signal, the second rotational speed differing from the first rotational speed.
A second aspect of this invention is based on the first aspect thereof, and provides a magnetic disk apparatus further comprising third means for reading a signal from the magnetic disk; fourth means for discriminating data from the signal read by the third means; fifth means for determining whether or not the fourth means normally discriminates the data from the signal read by the third means; and sixth means for, in cases where the fifth means determines that the fourth means normally discriminates the data, controlling the first means to unchange one of the first and second pulse-train signals which is currently generated by the first means, and for, in cases where the fifth means determines that the fourth means does not normally discriminate the data, controlling the first means to change one of the first and second pulse-train signals which is currently generated by the first means to the other of the first and second pulse-train signals.
A third aspect of this invention is based on the first aspect thereof, and provides a magnetic disk apparatus wherein the first means comprises means for generating a fixed-level signal in response to a motor stop signal, and the second means comprises means for, when the first means generates the fixed-level signal, stopping the spindle motor in response to the fixed-level signal.
A fourth aspect of this invention provides a magnetic disk apparatus comprising a spindle motor for rotating a magnetic disk; first means associated with the spindle motor for generating a first signal having a period which decreases as a rotational speed of the motor increases; second means for generating a second signal having a train of pulses, wherein a pulse frequency of the second signal is initially equal to a first frequency; third means for counting pulses in the second signal during every time interval corresponding to the period of the first signal, and generating a third signal depending on a total number of the counted pulses for every time interval corresponding to the period of the first signal; fourth means for generating a fourth signal representing a deviation of the third signal generated by the third means from a fifth signal being a reference signal; fifth means for controlling the rotational speed of the spindle motor in response to the fourth signal generated by the fourth means to nullify the deviation of the third signal from the reference signal; sixth means for reading a sixth signal from the magnetic disk; seventh means for detecting actual data in the sixth signal read by the sixth means; eighth means for determining whether or not the seventh means successfully detects the actual data; ninth means for, when the eighth means determines that the seventh means successfully detects the actual data, maintaining the pulse frequency of the second signal at the first frequency; and tenth means for, when the eighth means determines that the seventh means does not successfully detect the actual data, changing the pulse frequency of the second signal from the first frequency to a second frequency different from the first frequency to change the rotational speed of the spindle motor which is controlled by the fifth means.